#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<string.h>
#include<stdlib.h>
#include<sys/wait.h>

#define NUM 1024
#define SIZE 64
#define SEP " "

char cwd[1024];
char enval[1024];
int lastcode=0;

char *homepath()
{
    char *home=getenv("HOME");
    if(home) return home;
    else return (char*)".";
}

const char *getUsername()
{
    const char *name=getenv("USER");
    if(name) return name;
    else return "none";
}

const char *getHostname()
{
    const char* hostname=getenv("HOSTNAME");
    if(hostname) return hostname;
    else return "none";
}

const char *getCwd()
{
    const char* cwd=getenv("PWD");
    if(cwd) return cwd;
    else return "none";
}

int getUserCommand(char* command,int num)
{
    printf("[%s@%s %s]# ",getUsername(),getHostname(),getCwd());
    char* r=fgets(command,num,stdin);
    if(r==NULL) return -1;
    command[strlen(command)-1]='\0';
    return strlen(command);
}

void commandSplit(char* in,char* out[])
{
    int argc=0;
    out[argc++]=strtok(in,SEP);
    while(out[argc++]=strtok(NULL,SEP));
}

int execute(char* argv[])
{
    pid_t id=fork();
    if(id<0) return -1;
    else if(id==0)
    {
        execvp(argv[0],argv);
        exit(1);
    }
    else{
        int status=0;
        pid_t rid=waitpid(id,&status,0);
        if(rid>0)
        {
            lastcode=WEXITSTATUS(status);
        }
    }
    return 0;
}
void cd(const char* path)
{
    chdir(path);
    char tmp[1024];
    getcwd(tmp, sizeof(tmp));
    //sprintf(cwd, "PWD=%s", tmp); // bug
    putenv(cwd);
}

int doBuildin(char* argv[])
{
    if(strcmp(argv[0],"cd")==0)
    {
        char* path=NULL;
        if(argv[1]==NULL) path=homepath();
        else path=argv[1];
        cd(path);
        return 1;
    }
    else if(strcmp(argv[0],"export")==0)
    {
        if(argv[1]==NULL)
        {
            printf("\n");
            return 1;
        }
        if(*argv[1]=='$'&&strlen(argv[1])>1)
        {
            char* val=argv[1]+1;
            if(strcmp(val,"?")==0)
            {
                printf("%d",lastcode);
                lastcode=0;
            }
            else{
                const char* enval=getenv(val);
                if(enval) printf("%s",enval);
                else printf("\n");
            }
            return 1;
        }
        else{
            printf("%s\n",argv[1]);
            return 1;
        }
    }
    else if(0){}
    return 0;
}

int main()
{
    while(1)
    {
        char usercommand[NUM];
        char* argv[SIZE];
        int n=getUserCommand(usercommand,sizeof(usercommand));
        if(n<=0) continue;
        commandSplit(usercommand,argv);
        n=doBuildin(argv);
        if(n) continue;
        execute(argv);
    }


    return 0;
}